In electrical machining and electrical discharge machining in particular, the machine tool must sometimes carry a tool or workpiece electrode which is large in weight and size. When such an electrode is moved to progressively form a desired shape complimentary to the shape of the tool electrode in the workpiece, it is desired that a drive system for effecting this movement be capable of converting an input electrical drive signal into a corresponding mechanical displacement with precision and speed.
Fluid actuated servo feed systems have been recognized to entail errors in the machining operation due to the inertia inherently encountered by movable parts including the electrode and are now being increasingly replaced by digital servo systems operated with a stepping motor which assure a given servo feed with greater precision.
While the digital servo system can advantageously perform a desired electrode positioning with ease and allow precise ascertainment of a given electrode position, it has generally been recognized to be disadvantageous for use with a movable electrode which is large in weight and size because then not only is an expensive high-rating servo motor required but it still lacks a satisfactory operating stability. It has been proposed to provide the machining feed with a mechanical counterbalance but it has been found that this generally increases the inertia of the movable parts and substantially reduces the speed of operating in response to an input drive signal.